1. Field of the Invention
This invention relates to a method for improving the Theological properties of corn packaged-tortillas by using commercial Xylanase with antimicrobial acidic-additives during tortilla making.
2. Description of Related Art
High-quality masa flour can be produced by conventional techniques only if the food-grade dent corn has the following characteristics: uniformity in kernel size and hardness, low stress-cracks and kernel damage and ease of pericarp removal during the lime-water cooking process. Nixtamalized corn flour (NCF) is produced by alkaline cooking of corn, washing, grinding the nixtamal and drying to give corn masa flour. This flour is sieved and blended for different product applications and it is usually supplemented with additives before packaging for commercial table tortilla and snack production. MASECA is the main brand flour in the US and Latin America, followed by Minsa, Agroinsa, Ill. Cereal Mills (Cargill) and Quaker Oats (Sustain, 1997).
Although the pericarp or bran is partially removed during the alkaline-cooking and washing process stages, there is still fiber left from the corn kernel (U.S. Pat. No. 4,513,018; Montemayor and Rubio, 1983, Ramirez and Alvarez, 1995). According to Watson (1987), the corn pericarp makes up 5-6% of the kernel dry weight. It also contains 67% hemicellulose, 23% cellulose and 0.6% soluble-fiber (soluble-hemicellulose). Unlike whole wheat, in which soluble fiber amounts to 11% of the total fiber, the corn soluble fiber is negligible (1%). Primary cell walls from the aleurone and starchy endosperm (83% dry weight) consist predominantly of arabinoxylan, xcex2-glucan and some cellulose. It is estimated that mainly insoluble fiber in the pericarp and endosperm make up 78% of the total dietary fiber (9.5% in the kernel dry-weight).
Arabinoxylans are complex polymers (20,000-170,000 daltons) with a linear backbone of (1,4)-xcex2-xylopiranosyl units to which substituents are attached through 02 and 03 atoms of the xylosil residues (mainly, xcex1-L-arabinofuranosyl; Fincher and Stone, 1986). A high degree of arabinosylation will increase its water solubility and more than 20% of the water in wheat-flour dough is associated with arabinoxylans. This polymer is apparently linked to the cellulose skeleton in the corn cell wall by ester linkage cross-bonding through ferulic and diferulic acid.
Nixtamalized corn flour or masa flour can contain from 7-9% of total dietary fiber or bran and 6-8% mainly consists of insoluble fiber on a dry-weight basis (Sustain, 1997). Dietary fiber of the new generation can surpass the functional and sensory qualities of the standard dietary fibers (e.g., commercial source of wheat bran can be removed of its starch, gluten and phytic acid). Due to its new fiber structure and its capillary effect the new fiber has good water binding capacity (twicefold) and a positive effect on baked goods freshness (e.g., Vitacel-brand name).
Haarasilta et al. (U.S. Pat. No. 4,990,343), Bxc3xa1ez-Vxc3xa1squez and Schoefield (1993) and Tanaka et al. (U.S. Pat. No. 5,698,245) have proposed that the use of endo and exo-hemicellulases causes decomposition of wheat insoluble fiber. Van Der Wouw et al (U.S. Pat. No. 6,066,356) also reported the use of arabinoxylanases to degrade the water-insoluble-solids from maize, in the preparation of feed or food (degermed maize and debranned wheat for bread).
Native Cellulose and Hemicellulose would render the dough non-homogeneous and affect the dough stretching capacity by preventing the formation of a gluten network (e.g., gliadin which provides elasticity and glutenin which effects viscosity). The enzyme treated bread product has an increased volume, more uniform grain structure, slower aging (retarded staling or retrogradation) and a reduction or replacement in baking additives.
The benefit of using a xylanase instead of a traditional hemicellulase (pentosanase) preparation is that there are fewer side activities (e.g., xcex1 or xcex2-amylase, xcex2-xylosidase/glucosidase) in the xylanase product. A suitable level of enzymes results in a desirable dough softening without causing stickiness, thereby improving machinability.
Xylanolytic systems (Wong and Saddler, 1992) include xylanases (1,4-xcex2-D-xylan xylanohydrolase, EC 3.2.1.8) and xcex2-xylosidases (1,4-xcex2-D-xylan xylohydrolase, EC 3.2.1.37), the former generally hydrolyse the xylan backbone (endo-type) whereas the latter hydrolyse xylo-oligomers (exo-type). Xylose is not usually the major product and it is typically produced after xylobiose and xylotriose (smallest oligomer). Nonspecific xylanases from Trichoderma spp may attack cellulose and carboxymethylcellulose. Xylanases are classified into two major families (F or 10 and G or 11) of glycosylhydrolases. F10 xylanases are larger, more complex and produce low DP oligosaccharides (less specific); F11 are more specific for xylan (Jeffries, 1996). Low molecular weight xylanases (269-809 amino acid residues) were from B. Pumilus, B. Subtilis and C. Acetobutylicum (Wong and Saddler, 1992).
The xylanases can be prepared microbiologically by means of fungi and bacteria: A. Niger had shown not only arabinose releasing xylanase activity but also a xylotriose one, Trichoderma spp xylanases had optimal acitivity conditions between 45-65xc2x0 C. and pH 3.5-6.5, Bacillus spp had alkaline tolerant (up to pH 10) and extreme thermophilic xylanases; and a Thermotoga sp (strain FjSS3-B1) xylanase had a temperature optimum of 105xc2x0 C. at pH 5.5 and an half-life of 90 min at 95xc2x0 C.
In recent years there has been a growing interest in the use of xylanase enzymes in the paper, pulp (enhance beatability and binding ability), food and feed industries. The use of xylanases (with or without cellulase and pectinase) has been proposed for clarifying juices and wine, for extracting coffee, plant oils and xe2x80x9cstarchxe2x80x9d, for improving the nutritional properties of agricultural silage, for macerating plant cell walls, for producing food thickeners and for providing xe2x80x9ctextures to bakery productsxe2x80x9d. The scope for new applications is restricted mainly by the limited availability of specific xylanases with the required purity, properties (ie, pH optima and thermal stability) and action patterns (endo or exo-hydrolytic mechanisms). Commercial xylanase preparation marketed for pulp treatment include Pulpzyme HA (with little cellulolytic activity) from T. Reesei and Albazyme from T. Longibrachiatum. Crude enzyme preparations containing both hemicellulases and cellulases could be used to improve fibrillation and drainage properties of recycled pulpwood fibers (Wong and Saddler, 1992).
To aid in these developments, simple, reliable and sensitive procedures are required for the quantitative measurement of xylanase in a range of products with trace to high enzyme activity levels. The advent of genetic engineering has allowed the production of very specific enzyme preparations. A range of plant polysaccharides, including starch, xcex2-glucan, arabinoxylan, fructans, as well as starch damage can be measured (McCleary, 1992).
Lxc3x3pez-Munguxc3xada et al. (Mexican patent application: No. 952,200) describes an enzymatic process to produce corn tortillas which retard accelerated staling with texture improvement during four days frozen storage. A fungal xcex1-amylase blend (i.e., commercial enzymes from Novo, Gist Brocades and Genencor International) was added during rehydration of nixtamalized corn flour (0.01 U/kg), and modified the starch during tortilla cooking up to the denaturing temperature (Iturbe-Chixc3x1as et al., 1996).
The present invention relates to a method of improving the Theological properties of corn packaged-tortilla produced therefrom, by adding to the nixtamalized corn flour an effective amount of an enzyme component (or blend) containing a xylanase. A dough prepared with this flour premix will have advantageous Theological and handling properties and tolerance in a mechanized tortilla machine (Rodotec Ecolxc3x3gica-100; made by Tecnomaxc3xadz Gruma, Monterrey, N.L. Mxc3xa9xico). The final tortilla product will keep its flexibility and compressibility, even during extended commercial storage. The corn packaged-tortilla produced according to the invention therefore has less or no need of conventional antistaling or functional additives.
The dough is produced by combining nixtamalized corn flour, water, and a xylanase, with acidic-additives if desired, and mixing and kneading to form a suitable dough for traditional as well as mechanized tortilla production. The invention also comprises a novel packaged-tortilla premix which includes instant masa flour, antimicrobial acidic-additives, and enzyme preparation with a suitable carrier directly incorporated to the flour during its production.
Accordingly, the present invention provides a soft and cohesive dough without causing stickiness during tortilla manufacture. Another object is to provide a packaged-tortilla with improved flexibility and rollability during commercial storage. The main object of the invention is the application of a xylanase to improve the flexibility of packaged-tortillas. The baked product or corn tortilla is made by combining nixtamalized corn flour with a suitable amount of an enzyme preparation, antimicrobial acidic-additives and water for mixing or kneading to produce a soft and cohesive dough without excessive stickiness during mechanized tortilla production.
Preferably, the enzyme blend contains between 100 mg to about 1000 mg of a commercial xylanase per kilogram of corn flour. The packaged-tortilla premix preferably includes antimicrobial acidic-additives (0.5-1% weight based on flour) in combination with the enzyme blend before adding the premix directly to the flour in the production factory.
A tortilla can be defined as a flat, round, unfermented pancake produced from lime-cooked corn (Zea Mays L.). Three basic types of corn products are industrially manufactured: packaged-tortilla, corn and tortilla chips. Many manufacturers use corn masa flour because it does not require much labor, equipment, and processors do not have to pay as much for effluent disposal and control of production practices.
The enzyme blend comprises about 100 mg to about 1000 mg of xylanase per kilogram of corn flour and calculated as xylanase units. A commercial preparation of fungal hemicellulase from A. Niger was, kindly provided by Amano Pharmaceutical Co. and another multicomponent hemicellulase by Rhone-Poulenc (Rhodia). A crude cellulase preparation from T. Longibrachiatum (Fraction A: mainly with endoxylanase and cellulase activities) was obtained from Biotechnology Center (ITESM, Monterrey, N.L., Mxc3xa9xico: Bxc3xa1ez-Vxc3xa1squez and Schoefield, 1993).
The definitions of the different enzyme activities are defined below:
Xylanase activity (Megazyme International Ireland, Ltd. Ireland). A modified Somogyi-Nelson reducing sugar assay for the measurement of xcex2-xylanase using Wheat Arabinoxylan as substrate (Megazyme assay procedures XYL 9/95:14-15). One unit is the amount of enzyme which produces one micromole of xylose per minute at pH 4.7 and 40xc2x0 C. (Fraction A: test result 1,400 micromoles-xylose/min-g). The major advantages of this procedure are that the color response with oligosaccharides of increasing degree of polymerisation is stoichiometric; and the assay is very sensitive (10-50 xcexcg).
Rhodia-Rhone Poulenc reported a minimum xylanase activity (multicomponent hemicellulase) of 4,000 U/gram (4,000 mg-maltose/min-g) or reducing sugar equivalent to 5,850 xcexcmoles-glucose/min-g (DNS assay).
Hemicellulase activity (Amano-Enzyme USA. Co., Ltd.). A Somogyi-Nelson assay was used and one unit is the amount of enzyme which produces reducing sugar equivalent to ten micrograms of xylose per minute at pH 4.5 and 40xc2x0 C. (Amano-90: test result 109,000 U/gram or 7,270 micromoles-xylose/min-g).
The enzyme preparation may contain xylanase activity functioning both with endo and exomechanisms. They may also contain the following enzyme side-activities: xcex1-amylase (Amano-90), xcex2-xylosidase (Amano-90) and xcex2-glucosidase (Fraction A and Amano-90).